1. Field of the Invention
The present invention relates to a disk drive apparatus, a video camera apparatus, and a processing method for use with the disk drive apparatus for recording and playing back various types of data, including computer data and, in particular, to a disk drive apparatus capable of performing random access. More particularly, the present invention relates to a disk drive apparatus of a type which is installed and used in a host, such as a computer system or a portable video camera and, in particular, to a disk drive apparatus, a video camera apparatus, and a data processing method for use with the disk drive apparatus for recording and playing back computer data requiring data reliability, as well as video data and audio data requiring real-time characteristics.
2. Description of the Related Art
Various types of information processing systems, including general-purpose computers, have mounted therein a data recording and playback apparatus for storing large application software and large amounts of data in a non-volatile state. There are various recording and playback apparatuses, such as disk types, which hold data on a rotating disk, and tape types, which hold data on a winding-type tape. Of these, the disk-type recording and playback apparatus is superior in that random access is possible.
A typical disk apparatus is a hard disk drive (HDD). With advances in magnetic head technology and signal processing technology, the increased capacity of HDDs is remarkable. For example, in the period from about 1990 to the present, the recording density per unit area has continuously increased annually by about 60%. It is expected that 10 to 20 GB of data will be recordable on a 3.5-inch diameter disk sometime after 2000. That is, it is believed that one HDD having a plurality of disks will have a recording capacity exceeding 100 GB.
As described above, since an HDD has a large capacity, it is suitable for recording digital image information. On the other hand, with advances in recent image compression technology, the average data rate necessary for recording an image is progressively decreasing. For example, in the case of the MPEG2 (Motion Picture Experts Group Phase 2) standard which is predicted to be further used in the future in personal computers and digital satellite broadcasts, a moving image having satisfactory quality at an average data rate of approximately 4 to 8 Mbits/sec can be recorded and played back.
On the other hand, generally, there has been a demand for an HDD for use in computers to be constructed so as to realize a higher speed of data access. In a case where compressed moving-image data is recorded or played back in an HDD which is designed by assuming such computer uses, the data rate is higher than is necessary even if the head movement time between concentric recording tracks is taken into consideration. In other words, to record and play back compressed moving-image data in an HDD for use in computers, the disk rotation speed is higher than necessary, unfortunately causing a problem of large power consumption by the spindle motor or rotation noise arising from high-speed rotation.
One typical mode of a moving-image recording system is a portable video camera. Since a portable apparatus, such as a video camera, is battery-driven, reduction in power consumption is crucial to achieve extension of operation period.
As a conventional method for achieving a high speed at connection time to a computer while ensuring low power consumption during portable use, a magnetic disk playback method having a plurality of different operation modes of at least two of a low-speed mode and a high-speed mode is disclosed in Japanese Unexamined Patent Application Publication No. 10-162483, which is an application for patent by the same applicant as that of this application. A disk apparatus which uses a synchronization servo method as a head positioning servo method suitable for realizing a plurality of rotation speeds and which records image information and sound information, in particular, in a low-speed mode, is disclosed in Japanese Unexamined Patent Application Publication No. 10-261357, which is an application for patent also by the same applicant as that of this application.
Generally, in an HDD, one data file is discretely recorded and played back by being divided in packet units called data sectors, and error handling during recording and playback is also performed for each data sector. The disk of an HDD is generally rotating at a constant angular velocity (CAV), and the data rate differs depending on the data recording radius. Therefore, in order to ensure real-time continuity in recording and playback of image information and sound information, it is necessary for the average data rate in discrete recording and playback of data sectors to be higher than the data rate for the image and sound information.
If an extended period is spent on error handling for recording and playback of one data sector, the average data rate falls below a required level, and the continuity of image and sound information may be lost. In particular, in a case where the number of revolutions of the disk is reduced to lower consumption of the power, since there is no allowance for the data rate, this problem is likely to occur. However, since the occurrence of various errors is a probability phenomenon, and the error varies due to the use state and the use history on the HDDs, it is difficult to anticipate them completely at the time of design. Furthermore, in a conventional HDD, if an error occurs once, full use of the best technique available, such as correction and re-reading by error correction code, is made to read correctly, causing the error handling time to become prolonged. Therefore, there is a problem in that it is difficult to ensure real-time characteristics at the time of design.
As one of the error handling modes, which are factors hindering the ensuring of real-time characteristics, a processing operation for a retry may be mentioned. The recording and playback of data in an HDD are performed in units (for example, units of 512 bytes) of a short data sector corresponding to a packet in communication technology. The retry is an operation such that the same operation is performed again when an error occurs in a step of executing a command, such as recording and playback of data sectors, supplied from a host.
There are various types of causes of error which result in retries. First, an error in head movement (seek) to a target sector is cited. To overcome a seek error, the recording and playback of the target sector is abandoned and skipped, or a retry must be performed. Since a waste of time of approximately several msec to several tens of msec is necessary for one retry, this becomes a factor hindering real-time characteristics.
Next, there is a retry (write retry) during data recording. In a case where it is detected that the position variation of a head from a data track exceeds a permissible amount, for example, due to a mechanical impact applied from outside the HDD while recording on one data sector is being performed, the recording operation is stopped. Thereafter, after awaiting the recovery of the head position variation to a normal state and the reaching of the subject sector directly below the head again as a result of the disk rotation, a data recording operation on the subject data sector is performed again (write retry).
Furthermore, in a case where an error in an amount exceeding correction performance by an ECC (Error-Correction Code) added to a sector occurs when one data sector is played back in a retry (read retry) during data playback and it is determined that correction is impossible, after awaiting the reaching of the subject sector directly below the head again as a result of the disk rotation, a playback operation of the subject logical sector is performed again (read retry). In addition, in a case where it is determined again that correction is impossible even if a read retry is performed once, a second read retry is performed. In a case where an error is not a soft error due to a random cause, such as noise, but is an error due to a definite cause, such as a scratch in the magnetic film on the disk, the disk cannot be read correctly even if read retries are performed, for example, 10 or more times, and a waste of time of 100 msec or more is necessary, fatally hindering the ensuring of real-time characteristics.
Since the maximum number of times the above various retries are executed and other error handling methods are conventionally fixed by HDD design, it is not possible to appropriately perform control according to the state of the entire disk recorder.
Also, although a means for completely permitting or prohibiting the execution of a retry is conventionally provided (for example, part of the ATA (AT-Attachment) interface standard prepared by the ANSI (American National Standards Institute), a means for appropriately setting a maximum permissible time required for error handling, and a means for dynamically performing control according to the urgency (that is, demand for real-time characteristics) of recording and playback are not provided.
In the manner as described above, there is generally a demand for an HDD to perform high-speed access and an accurate recording and playback process in computer uses, while in moving-image data processing, real-time characteristics are important. Furthermore, in moving-image data processing using a portable video camera, there is the problem of minimizing power consumption. Although the minimization of power consumption can be realized by decreasing the rotation speed of the HDD, if a prolonged period is spent on error handling by decreasing the number of revolutions of a disk, continuity of image information and sound information is lost.